A commutator for an electric motor typically comprises a plurality of commutator bars electrically connected to a plurality of hooks, wherein the hooks are used to mount one or more coils, so that the coils are electrically connected to the commutator. In many commutators, the commutator bars and hooks are integrally formed from a stamped copper sheet. However, in electric motors using carbon brushes, the hardness of the carbon brush is much less than that of the copper commutator bars and hooks, which leads to increased wear and tear on the carbon brushes during motor operation.
To address this problem, some commutators use graphite in place of copper in the commutator bars. However, this may create problems when connecting the graphite commutator bars to the copper hooks. In the current industry, a nickel or copper metal layer is formed on the surface of the graphite bars through electroplating or ion sputtering. Subsequently, a solder material having a melting point of 450 degrees Celsius (° C.) or less, such as tin, is used to solder a copper sheet comprising the plurality of hooks to the metal layer on the graphite bars. However, due to there being no metallurgical bond between the metal layer and graphite bar, the connection between the metal layer and graphite bars in commutators manufactured using this method lack sufficient strength.
Alternatively, a brazing material with a melting point of 450° C. or higher is applied between the graphite bars and the copper sheet, where the graphite bars, copper sheet, and brazing material are placed in a high temperature furnace and brazed, fixing the copper sheet to the graphite bar. However, due to the large differences of coefficient of thermal expansion between copper and graphite, the brazing process may cause many large cracks to form in the graphite. In addition, the copper of the copper sheet may be weakened or softened by the high temperature brazing process, making it less suitable for mounting the coils.
Accordingly, there exists a need for a method for manufacturing a commutator that addresses the above problems.